Posted on October 09, 2013 at 15:43Hi,
I'm using the STM32L151 for a project which needs some reasonably precise (~0.1%) voltage measurements. I'm measuring the micro's 3V3 supply by converting the internal reference and using the factory programmed VREFINT_Factory_CONV value, which I believe is set at the factory by converting the reference with Vcc=3.000V.
I see errors as large as 20mV in my 3.3V supply measurement on some boards, some boards are spot-on. Any suggestions as to why I get such a large error? I would have hoped that the error would have been of the order of the total unadjusted ADC accuracy which is about 5 bits (=4mV).
Everything is at room temperature. I'm using the longest ADC sample time.
This is the maths:
f32_3V3 = 3.0f * (float)(*(uint16_t*)VREFINT_Factory_CONV) / (float)ADC_Value;
Cheers,
Mark
#vrefint-adc
